Optimize the preparation of Fe3O4-modified magnetic mesoporous biochar and its removal of methyl orange in wastewater

In this paper, Eichhornia Crassipes stems were used as biomass feedstock, and Fe 2+ was used as the precursor solution to prepare Fe 3 O 4 -modified magnetic mesoporous biochar (Fe 3 O 4 @BC). By using Box-Behnken design (BBD) response surface methodology, the influences of three preparation parameters (X 1  = Fe 2+ concentration, X 2  = pyrolysis temperature and X 3  = pyrolysis time) on the adsorption of methyl orange (MO) by Fe 3 O 4 @BC were investigated, and a reliable response surface model was constructed. The results show that X 1 X 2 and X 1 X 3 have a significant influence on the adsorption of MO by Fe 3 O 4 @BC. The surface area and pore volume of Fe 3 O 4 @BC are controlled by all preparation parameters. The increase of pyrolysis time will significantly reduce the -OH on the surface of Fe 3 O 4 @BC and weaken its MO adsorption capacity. Through the numerical optimization of the constructed model, the optimal preparation parameters of Fe 3 O 4 @BC can be obtained as follows: Fe 2+ concentration = 0.27 mol/L, pyrolysis temperature = 405 °C, and pyrolysis time = 3.2 h. The adsorption experiment shows that the adsorption of Fe 3 O 4 @BC to MO is a spontaneous exothermic process, and the adsorption capacity is maximum when pH = 4. The adsorption kinetics and adsorption isotherms of Fe 3 O 4 @BC to MO conform to the pseudo-second-order kinetics and Sips model, respectively. Mechanism analysis shows that electrostatic interaction and H bond formation are the main forces for Fe 3 O 4 @BC to adsorb MO. This research not only realizes a new way of resource utilization of Eichhornia Crassipes biomass but also enriches the preparation research of magnetic biochar.